2.13. HE staining
The aorta was fixed, dehydrated, and embedded with OCT before continuous sectioning using a frozen section machine (CryoStar NX70 HOMVPD, Thermo). Frozen sections were equilibrated at room temperature for 10min, stained with hematoxylin for 4min, and rinsed with running water for 10min; then stained with 1% eosin solution for 2min, and rinsed with running water for 30s. The sections were subjected to gradient alcohol for rapid dehydration, then cleared using xylene I, xylene II and xylene III for 5min, respectively. The sections were sealed with neutral resin and imaged by microscopy (Olympus,Tokyo, Japan).